The present invention relates to a photosensitive resin composition and a photosensitive element using the same.
In the art of manufacture of printed circuit boards, photosensitive elements made of photosensitive resin compositions with a support and a protective film have been popularly used as resist in such treatments as etching and plating.
A printed circuit board is manufactured by a process comprising the steps of laminating a photosensitive film on a copper substrate, subjecting it to pattern exposure, removing the unexposed portion with a developer, carrying out etching or plating to form a pattern, and then stripping the cured portion from the substrate.
An alkaline developer comprising a sodium bicarbonate solution or the like is popularly used as developer for removing the unexposed portion. Usually developer is used as long as it maintains the ability to dissolve the photosensitive layer to a desired degree, and in use thereof, the photosensitive resin composition is dissolved or dispersed in the developing solution.
With the recent trend toward higher density of printed circuit boards, which entails reduction of contact area between the copper substrate and the pattern-formed photosensitive layer, it is required of the composition used for forming the photosensitive layer to show excellent adhesiveness, mechanical strength, chemical resistance and flexibility in the development, etching or plating step.
For the improvement of chemical resistance, methods using a photopolymerizable compound having isocyanurate rings are disclosed in JP-A-61-77844, JP-A-62-290705, JP-A-61-14212, JP-A-59-222480, JP-A-1-14190, JP-A-57-55914, JP-A-5-216224, JP-A-5-273754, etc., but these methods have the problem that the cured film of said compound is hard and frangible.
On the other hand, from the viewpoint of improvement of processability, a photosensitive resin composition having high sensitivity and little possibility of causing contamination of the plating bath is desired, but these properties are dependent on the type and amount of the photoinitiator used in the composition.
High-sensitivity photoinitiators are disclosed in DE-AS 2027467, EP-A 11786, EP-A 220, EP-A 589, JP-A 6-69631, etc., but these photoinitiators have the disadvantage that they may cause contamination of the plating bath.
Photoinitiators with low possibility of causing plating bath contamination and high sensitivity are proposed in JP-A-60-239744, JP-A-2-226149, etc., but they are at a disadvantage in that their sensitivity is low.
U.S. Pat. No. 3,479,185 discloses a photosensitive resin composition comprising a 2,4,5-triphenylimidazole dimer, which is a photoinitiator with low possibility of causing plating bath contamination, combined with a hydrogen donative compound to elevate sensitivity. This composition, however, has the drawbacks that in case sensitivity of the composition has been adjusted to a desired level, when the amount of said 2,4,5-triphenylimidazole dimer used is increased, the line width of the resist is enlarged, while when the amount of the hydrogen donative compound is increased, adhesiveness to copper and storage stability are deteriorated.
Combination of a 2,4,5-triphenylimidazole dimer and a compound having a highly reactive ethylenically unsaturated group (such as polyethylene glycol dimethacrylate) has also been studied, but this combination is very poor in chemical resistance.